The present invention relates to three-dimensional graphics and, more particularly, to a system and method for combining volume rendering and segmentation in three-dimensional graphics generation.
In three-dimensional (3D) imaging, segmentation is employed, which is a process for identifying, outlining, and/or demarcating volumes of interest from a 3D volume dataset. The volumes of interest in a 3D medical application, such as tomographic analysis, are typically organs. Segmentation may be used for measurements of, for example, the diameter of a blood vessel or other tubular tissues of a patient. In addition, segmentation may be used to navigate through space, including virtual space, with the boundary regions of a segmented organ being used for automatic navigation. Through segmentation, visualization of organs may be performed, in which segmented organs are converted into surface models which may be rendered at a high frame rate using graphics computers and/or software.
Segmentation may be performed using various techniques, such as simple thresholds applied on the entire volume of the 3D image, for example, to segment bones. Also, adaptive thresholds may be used to prevent xe2x80x9cbleedingxe2x80x9d from one portion of the 3D image to another. In addition, contours may be drawn on every slice of the object being imaged, such as an organ. Such segments are then displayed for viewing by the viewer.
Volume rendering is also performed in 3D imaging, in which the intensity values of the voxels of the 3D image are converted into opacity values using a specified mapping. Other possible mappings include intensity to (color plus) opacity as well as intensity gradient to opacity. The opacity values are then used to render the entire volume or a part thereof on a display screen. Each screen pixel is assigned a particular value depending on the opacity of all of the voxels which are projected onto the respective screen pixel. A user typically adjusts the mapping of intensity to opacity, for example, to enhance features, and/or the user may change the viewing position and/or direction to change the displayed view, which may necessitate redrawing the 3D image and updating the intensity and opacity values.
It is known that visualization and segmentation of 3D images may be combined to allow a user to interactively view the segmentation and to interactively guide the segmentation process. Such combinations have employed segmentation using global thresholds and visualization using surface shaded displays.
Heretofore, volume rendering and segmentation have not been effectively combined since volume rendering did not permit functions or tools such as measurement, automatic navigation, etc. through a 3D image, while traditional surface rendering methods using pre-segmented data could perform such functions or tools.
Thus, there is a need for a volume rendering system and method which provides such functions as measurement and automatic navigation.
A three-dimensional (3D) imaging system and method include a processor for generating a volume-rendered 3D image on a display using a plurality of voxels from a 3D image dataset; and a view selector which responds to user inputs for determining a first set of voxels corresponding to a boundary in the volume-rendered 3D image using a predetermined boundary-specifying criteria applied to a function of the opacity of the plurality of voxels. The processor responds to the first set and to a user function selection by performing the selected function to modify the volume-rendered 3D image relative to the detected boundaries. The selected function is a display function, a measurement function, or a segmentation function. The view selector determines the boundary from voxels having opacities greater than a predetermined threshold, or determines the boundary from voxels having a gradient in opacities greater than a predetermined threshold. Alternatively, the view selector determines the boundary from voxels having a greatest contribution to a total intensity which is a function of the opacities of the voxels, or determines the boundary from voxels having respective contributions greater than a predetermined threshold, with such contributions being to a total intensity which is a function of the opacities of the voxels.
The disclosed system allows a user to manipulate the opacity mappings using trapezoids, sliders, etc. to be used to segment the volume. The system takes advantage of the fact that, when a user changes parameters to highlight a particular region, such parameters are sufficient to automatically determine which 3D points the user is actually looking at. It is also possible to restrict the volume of interest using, for example, cutplanes and other known volume region-selecting techniques, and then the disclosed system is applied to such a restricted volume.